Punita Thadani, it is a myth that thumb sucking and diet are related. It is an involuntary activity that some children take to. Even my daughter used to suck her thumb. Iv been to many doctors, dentists, homeopaths and all have advised me that it is ok if it is comforting to the child and also that till the age permanent teeth come it is of no real concern. I tried many things, but nothign worked. At 3+ years now, I have started putting a medical tape on her thumb (only a tape and no medicines) and sometimes a medicine by the name of Femite. it is a very bitter medicine, but useful only around the age of 2. 5 years or 3 years when children develop a taste for things and hate bitter things. When i used femite earlier, my daughter used to lick it off. but now at 3, she hates it. Also, i checked with dentists.. there are mouth appliances that come which can be implanted in the mouth of a child, but only around the age of 78 years. do not worry too much. just ensure hygiene as in she shouldnt put her thumb in the mouth after playing in sand etc.